1. Field of the Invention
The present invention relates to a process for producing mono- and/or di-chloro.beta.-trifluuoromethylpyridine (hereinafter referred to as the chloro.beta.-trifluoromethylpyridine) with industrial advantages by fluorinating mono- and/or di-chloro.beta.-trichloromethylpyridine (hereinafter referred to as chloro.beta.-trichloromethylpyridine) in the presence of a catalyst in a vapor phase.
2. Description of the Prior Arts
Chloro.beta.-trifluoromethylpyridines have been found to be converted into important compounds having excellent physiological activities and have been considered as important intermediates for agricultural chemicals and medicines. 2-Chloro-5-trifluoromethylpyridine is an especially important intermediate for herbicides, insecticides and fungicides. Therefore, it has been required to find an industrial process for producing such compounds in a mass production and an economical manner.
Thus, not many reports have been found for production of chloro.beta.-trifluoromethylpyridines, since the utilities of said compounds have not been considered to be important.
A fluorination of the chloro.beta.-trichloromethylpyridine can be considered for the production of the chloro.beta.-trifluoromethylpyridine. However, it has been considered that the chloro.beta.-trichloromethylpyridine as the starting material is not easily produced. For example, it has been described that a chlorination of methyl group of .beta.-picoline is difficult in HELVETICA CHIMICA ACTA, Vol. 59, Fase 1, Nr. 19-20, 1976. Therefore, it has not been known to produce chloro.beta.-trifluoromethylpyridines in a practical and industrial process.
Recently, it has been proposed to produce said chloro.beta.-trifluoromethylpyridines in European Pat. No. 0000483 and WO 79/00094 etc. In these prior arts, only experimental small scale processes are disclosed. For example, WO 79/00094 disclosed the following processes for producing 2-chloro-5-trifluoromethylpyridine;
(1) the process of the reaction of 2-chloro-5-trichloromethylpyridine with antimony trifluoride in a liquid phase at 140.degree. to 145.degree. C. for 1 hour;
(2) the process of the reaction of 6-chloronicotinic acid with sulfur tetrafluoride in the presence of hydrogen fluoride in a liquid phase in an autoclave at 120.degree. C. for 8 hours; and
(3) the process of the reaction of 2-chloro-5-trichloromethylpyridine with hydrogen fluoride in a liquid phase in an autoclave at 200.degree. C. for 100 hours.
These processes, however, have not been industrially applied for the following reasons: In the process (1) the expensive antimony trifluoride is used and causes trouble in a treatment of a waste solution. In the processes (2), (3), the reactions are respectively carried out under an elevated pressure taking a long reaction time. In the process (2), sulfur tetrafluoride which is toxic to men and beasts is used.
The inventors have studied the fluorination of the chloro.beta.-trichloromethylpyridine by reacting the chloro.beta.-trichloromethylpyridine with hydrogen fluoride at elevated temperature in a vapor phase without a catalyst. The desired result has not been accomplished. The inventors have further studied the fluorination by using activated carbon which has been often used in such fluorinations. The desired result has not been also accomplished. The inventors, however, have found the fact that the fluorination is smoothly performed in the presence of a specific catalyst to produce the chloro.beta.-trifluoromethylpyridine in high yield.